1. Field of the Invention
The present invention relates to a system for providing explicit routing functions in a connectionless network.
2. Background
The flow of data through a connectionless network is accomplished by transmitting data from one node (or router) to the next until the destination is reached. Typical routing protocols allow each router to determine the best path for forwarding data toward its destination. Each router performs calculations to determine the next hop router based on the known network topology. In link-state routing protocols, the existence of various nodes and connections (or links) in a network are advertised to other routers in the network. Thus, each router learns the topology of the network. Knowledge of the network topology is used by each router to determine the best "next hop" router for a particular destination.
All routers in the network or area perform similar calculations to identify the best next hop router for each destination in the network. The routers use this information to forward data to the destination specified.
An example of a link-state routing protocol is the Open Shortest Path First (OSPF) routing protocol. Each router running the OSPF protocol maintains an identical database describing the network topology. Using this topology database, each router is able to generate a routing table by constructing a shortest-path tree with the router at the root of the tree. OSPF is a dynamic routing protocol; i.e., OSPF detects changes in network topology and recalculates paths based on the new topology. Typically, all routers in an autonomous network run the OSPF protocol simultaneously. OSPF allows multiple networks and routers to be grouped together. These groupings are commonly referred to as areas. Each OSPF router generates link state advertisements (LSAs) describing the local state of its links. Each LSA is flooded (or broadcast) throughout the area. The area's topology database consists of the LSAs broadcast throughout the area.
The specific topology of a particular area is not broadcast to other areas. Instead, a summary of the area is transmitted to other areas, thereby reducing the amount of link-state information transmitted through the network. When a router is connected to more than one area, it maintains a separate topology database for each connected area. A separate execution of OSPF's basic routing algorithm is performed in each area. Additionally, routing within a particular area is determined only by the topology of the particular area. Each area may use a different authentication scheme, such that some areas may use stricter authentication schemes than other areas.
MOSPF is a multicasting extension to OSPF (a unicast routing protocol). Multicasting is the distribution of datagrams from a source to multiple destinations. The multiple destinations may be members of a multicast group such that each member of a multicast group receives datagrams addressed to the group. By adding a new type of LSA, the group membership LSA, MOSPF is able to determine the location of all multicast group members in the network.
Another type of LSA which may be supported by OSPF is the Opaque LSA. The Opaque LSA provides a general mechanism to permit future extensions of the OSPF protocol.
As link state routing protocols develop, new types of link state advertisements are created and existing link state advertisement formats are expanded or extended. New types of advertisements and extensions of existing advertisements increase the amount of data which must be exchanged between routers in a network. The increased data generates additional traffic on the network and requires additional memory or storage space within each router to store the new data. Furthermore, the increased number of advertisements requires additional calculation by the routers to process the advertisements.
If the level of data generated and transmitted through the network in the form of advertisements becomes too large, overall network performance may be reduced. Network routers may utilize a significant portion of their resources generating, receiving, processing and storing advertisements.
It is therefore desirable to provide a system for reducing the amount of router resources used to generate and process network advertisements.